Field of the Invention
The invention relates to a device for suspending a turbojet, in particular under a wing, and it relates more particularly to an improvement of an attachment between the turbojet and the pylon connected to the structure of the airplane. A so-called “middle” attachment of this kind is intended more particularly to take up thrust. By way of example, such an attachment is arranged between a front attachment connected to the casing of the fan and a rear attachment connected to the outer shroud of the exhaust casing.
Description of the Related Art
In a bypass turbojet as described for example in FR 2 925 016, the incoming air is compressed by the fan rotor and then split into two streams referred to as a core stream and as a bypass stream, that are cylindrical and coaxial. The bypass stream flows around the engine proper and is ejected downstream in order to provide a large fraction of the thrust. The core stream is subjected to compression before reaching the combustion chamber where it is mixed with fuel. The mixture is burnt in order to produce hot gases that feed successive turbine stages that drive the compressors and the fan. The core stream is also ejected into the center of the cold air flow in order to provide some of the thrust. The ratio of the flow rates of the bypass stream and of the core stream is referred to as the bypass ratio. The ratio of the diameters of the fan casing and of the engine casing is an important parameter for obtaining a high bypass ratio.
Such a turbojet is fastened by means of a support structure known as a pylon, e.g. under a wing.
When it is desired to increase the bypass ratio, it is necessary to define a turbojet in which the fan occupies a very large amount of space. In order to be able to install such a turbojet of very large diameter, it is necessary to approach the axis of the turbojet to the structure that carries it (typically a wing). Consequently, the space available for the pylon and for fastening attachments thereto is small.
The above-mentioned prior document describes in particular an isostatic middle attachment that is said to provide “total protection” that is suitable for preventing the turbojet becoming separated from its pylon. That middle attachment comprises in particular two links that are arranged symmetrically on either side of a vertical midplane between the hub of the front casing and the rear attachment or directly to the pylon, in the vicinity of the rear attachment.
Those two links are mounted via hinge connections to a yoke that is itself hinged to a base that is fastened to the rear attachment or to the pylon.
The yoke presents a transverse width such that it can also have hinge connections with clearance at the ends with lateral extensions of the base. In the event of a link breaking, the clearance existing between one of the extensions and the yoke is consumed. The forces are redistributed and then pass via the remaining link. If the break takes place in the central connection between the yoke and the base, both of the extensions take up the forces. That is why the attachment is said to provide “total protection”, since the breakage of any one element leads to a new distribution of force paths, preventing total breakage of the attachment.
Nevertheless, in order to accommodate an increase in the diameter of the fan, it is desirable to reduce the size of such an attachment under the pylon. Furthermore, in the known system as described in FR 2 925 016, it is also necessary to provide empty space between the pylon and the turbojet in order to be able to dismantle the attachment, since the attachment is oriented generally radially relative to the engine axis. In addition, that known attachment is relatively complex and expensive.